Spark ignition systems for internal combustion engines

ABSTRACT

A spark ignition system for an internal combustion engine has a pick-up producing a waveform controlling a trigger circuit which produces the required sparks. Below a predetermined engine speed, the spark is always produced at the same point on the waveform, but above the predetermined engine speed the spark is produced at a point on the waveform dependent on engine speed so that an automatic advance is obtained.

United States Patent Mainprize Aug. 19, 1975 SPARK IGNITION SYSTEMS FOR 3.314407 4/1967 Schneider 123/148 E INTERNAL COMBUSTION ENGINES 3,592 l78 7/l97l SChiff l23/l 17 R R27 477 6/1967 Piteo 123/148 E [75] Inventor: David Mainprize, Polesworth.

England Primary bxammerWendell E. Burns l l Asslgneei l Electl'lcal p y Llmlted, Assistant Examiner.lames W. Cranson, Jr. Birm ng a Eng Attorney, Agent, or Firm-Holman & Stern [22] Filed: May 30, 1973 pp 65,153 [57] ABSTRACT A spark ignition system for an internal combustion en- [30] Forelg Apphcatlon Pnorny Data gine has a pick-up producing a waveform controlling a June 14, 1972 United Kingdom 27788/72 trigger circuit which produces the required sparks.

Below a predetermined engine speed, the spark is al- [52] U5. CL. 123/148 E ways produced at the same point on the waveform, [5 l 1 Int. Cl. F02P 3/06 but above the predetermined engine speed the spark is [58] Field of Search 123/148 E, 117 R produced at a point on the waveform dependent on engine speed so that an automatic advance is ob- [56] References Cited tained.

UNITED STATES PATENTS 8 Cl 2 D F 2.785.215 3 1957 Yetter 123/148 E rawmg 'gures 13} Eli: /Z6

PATENTED AUG-1 9197s SHEET 1 [IF 2 PATENTED M181 9 I975 3.900.015

SHEET 2 [IF 2 SPARK IGNITION SYSTEMS FOR INTERNAL COMBUSTION ENGINES This invention relates to spark ignition systems for internal combustion engines.

A system according to one aspect of the invention comprises a pick-up driven by the engine and producing a waveform which controls a trigger circuit to produce the required sparks, the trigger circuit operating to produce a spark at a predetermined point on said waveform provided that the engine speed is below a predetermined level, but at engine speeds above said level the trigger circuit operating when it receives a predetermined input voltage from said pick-up, so that above said level an advance in timing is obtained with increasing engine speed.

A system according to another aspect of the invention comprises a trigger circuit biased to a first state, an engine driven pick-up coupled to the trigger circuit and which operates in a cycle during which it produces a voltage in opposition to said bias so that at a point in the cycle dependent on engine speed, the pick-up overcomes said bias to drive the trigger circuit to a second state and so produce a spark, and means operable when the engine speed is below a predetermined value for modifying the input from the pick-up to the trigger circuit whereby the trigger circuit is driven to the second state at a substantially constant point on the pick-up waveform.

Preferably said point is when the pick-up voltage is at its maximum. For this purpose, the voltage produced by the pick-up and having the same polarity as the bias is preferably used to charge a capacitor, the voltage of which is then applied to the trigger circuit in opposition to the pick-up voltage to obtain the required fixed timing, means being provided for preventing the capacitor from opposing the pick-up voltage above the predetermined engine speed. Preferably, a voltage sensitive device prevents charging of the capacitor above the predetermined engine speed.

Preferably, the system has a negative earth, and the capacitor is charged by the positive going output of the pick-up, the negative going pick-up output producing the required sparks.

In the accompanying drawings:

FIG. 1 is a circuit diagram illustrating one example of the invention, and

FIG. 2 illustrates the waveform of the pick-up used in FIG. 1.

Referring to FIG. 1, there are provided positive and negative supply lines l1, 12, the line 11 being connected through a resistor R6 and the vehicle ignition switch 13 in series to the positive terminal of the vehicle battery 14, and the line 12 being connected to the negative terminal of the battery 14, which is earthed. There are further provided a pair of terminals 15, 16 which are connected to the negative and positive output terminals of an electro-magnetic pick-up 28 driven by the engine. The lines 11, 12 are interconnected through a pair of resistors R2 and R3 in series, and the junction of the resistors R2 and R3 is connected through a diode D1 and a resistor R1 in series to the terminal 15. The junction of the diode D1 and resistor R1 is connected through a resistor R5 to the line 12, and is also connected to the emitter of an n-p-n transistor TR1 having its collector connected to the line 11, and its base connected to the line 11 through a resistor R4. The emitter of the transistor TR1 is connected to the line 12 through a resistor R5.

The lines 11, 12 are further interconnected through a series circuit including a resistor R7, a resistor R8, a diode D5 and a resistor R9, the junction of the diode D5 and resistor R9 being connected through a Zener diode D4 to the line 11, and through a capacitor C l to the emitter of the transistor TRl. The junction of the resistors R7 and R8 is connected through a resistor R10 to the base of an n-p-n transistor TR2, the emitter of which is connected to the line 12 through a resistor R13, and is also connected through a pair of diodes D3 and D2 in series to the base of the transistor TRl. The base of the transistor TR2 is connected through a resistor R11 and the capacitor C5 in series to the line 12, and the junction of the resistor R11 and capacitor C5 is connected to the terminal 16. The resistor R11 is bridged by a capacitor C2, and the base and emitter of the transistor TR2 are interconnected by a capacitor C4. The collector of the transistor TR2 is connected through a resistor R12 to the junction of the resistor R6 and the ignition switch 13.

The collector of the transistor TR2 is further connected through a capacitor C3 to the line 11, and is also connected to the base of a p-n-p transistor TR3, the emitter of which is connected to the line 11 and the collector of which is connected through a resistor R14 to the line 12. The collector of the transistor TR3 is also connected through a resistor R17 to the base of an n-p-n transistor TR4, the emitter of which is connected to the base of an n-p-n transistor TRS having its emitter connected through a resistor R18 to the line 12. The collectors of the transistors TR4 and TR5 are interconnected, and are connected to the junction of the resistor R6 and the switch 13 through a resistor R19, and to the collector of the transistor TR2 through parallel circuits one of which contains the resistor R15 and the other of which contains a resistor R16 and a capacitor C6 in series. The junction of the resistors R15 and R19 is connected to the line 12 through a Zener diode D6, and the emitter of the transistor TR5 is connected to the base of an n-p-n transistor TR6 having its emitter connected to the line 12, and its collector connected to the junction of the resistor R6 and switch 13 through a series circuit including the primary windings 21, 22 of a pair of ignition coils 23, 24 having respectively secondary windings 25, 26 connected to a pair of spark plugs associated with the engine. Finally, the collector and emitter of the transistor TR6 are interconnected by a Zener diode D7.

With the engine off and the switch 13 closed, current flows through the resistor R4 and most of the current then flows through the diodes D2, D3 and the resistor R13. However, the transistor TRl is just turned on, and its emitter current flows through the resistor R5, but also through the resistor R1, the winding 28 between terminals 15, 16 and the resistor R11 to the base of the transistor TR2.

Current also can flow through the resistor R6, the resistor R7 and the resistor R10 to the base of the transistor TR2, and the arrangement is such that the transistor TR2 is biased so that it conducts just sufficiently to turn on the transistor TR3, which in turn switches on the transistors TR4, TR5 and TR6 so that current flows in the windings 21 and 22. At the instant when a spark is required in one of the two cylinders of the engine, the transistor TR2 is turned off in a manner to be described, and so the transistors TR3, TR4, TRS and TR6 all turn off and both the ignition coils 23 and 24 produce a spark. Only one of these sparks would actually be required of course, but for convenience both ignition coils produce a spark at the same time, and the ignition spark produced by one of the coils will have no effect on the operation. The biasing current for the transistor TR2 is determined primarily by the resistors R7, R8 and R9 and the diode D5, the purpose of the diode D being to compensate for the base-emitter diode of the transistor TR2 so that the bias current does not change substantially with temperature.

When the transistors TR2, TR3, TR4, TRS, and TR6 turn off, the feedback provided by way of the resistor R16 and capacitor C6 ensures that the switching action is rapid. The resistor R ensures that after a spark has been produced, the bias current to the transistor TR2 must rise to a value slightly in excess of the value at which the transistor TR2 turns off before the transistor TR2 conducts sufficiently to turn on the transistor TR3 again, so that current flow in the windings 21 and 22 is re-established. The capacitors C3, C4 and C5 are to suppress interference feedback, and the diodes D6 and D7 protect the transistors TR4, TR5 and TR6 from excessive voltages in the system, and also from the possibility of damage if the system is incorrectly connected to the supply.

The electro-magnetic pick-up 28 is designed to produce sparks at the required instant of time, and the waveform produced by the pick-up 28 is shown in FIG. 2. It will of course be appreciated that although the general shape of the waveform will be the same at all engine speeds, the amplitudes involved will increase with increasing engine speed. The lines 31, 32 in FIG. 2 represent the potentials on the lines 12, 11 respectively in FIG. 1, and the line 33 represents the potential necessary at the base of the transistor TR2 to turn it off.

The diode D4 conducts permanently in use, and when the pick-up 28 is producing a positive going voltage, current flows from the terminal 16 through the resistor R11 and the base-emitter of the transistor TR2 to increase the conduction of the transistor TR2, so that the transistors TR3, TR4, TRS and TR6 all remain conducting. Current flowing through the transistor TR2 increases its emitter potential, so reducing conduction of the diodes D2, D3 and so increasing conduction of the transistor TRl which charges the capacitor C1. The values of the various components are so chosen that as long as the engine speed is below a predetermined value, the amplitude of the pick-up output does not saturate the transistor TR2, and the capacitor C1 charges to approximately the peak positive voltage of the waveform from the pick-up. As long as the engine speed is below the predetermined value, this voltage will be less than the voltage of the battery. It will be appreciated that FIG. 2 shows the situation where the speed of the engine is above the predetermined value, so that the pick-up voltage exceeds the battery voltage.

When the pick-up 28 is producing a negative going voltage, the positive voltage across the capacitor C1 is added to the pick-up voltage, and since the capacitor C l discharges only slightly during the period when the pick-up voltage changes from positive-going to negative-going, the capacitor C1 will hold the transistor TR2 on until the peak negative-going voltage is reached. This represents the slow speed position shown at 34 in FIG. 2, and so it will be seen that as long as the engine speed is below the predetermined value, the timing is fixed, and each spark occurs at the lowest negative voltage of the output from the pick-up.

When the engine speed is above the predetermined value, then when the pickup winding 28 produces a positive voltage, the amplitude of this voltage is sufficient to saturate the transistor TR2 so that the capacitor C1 is charged to the supply voltage of line 11. As a result, the negative going peak resulting from the voltage appearing at terminal 15 of pick-up coil 28 turns off the transistor TR2 when the negative output reaches a set value. The time taken for this set value to be reached is dependent on engine speed, so that an advance characteristic will be obtained of the form shown in 'FIG. 2, where the instant of firing can be anywhere between points 34, 35 in the waveform.

The above description ignores the presence of the capacitor C2. The proportion of the pick-up voltage which is applied to the base of the transistor TR2 is determined by the resistors R10, R11 and R1, and the capacitor C2 shunts part of this potential divider, so that at high speeds the base of the transistor TR2 receives a larger proportion of the output voltage of the pick-up waveform than at low speed. This produces an increased advance at high speeds, and the effect is enhanced by the distortion and advance of the wave form applied to the base of the transistor TR2 by virtue of the phase shift caused by the capacitor C2.

I claim:

1. A spark ignition system for an internal combustion engine comprising a pick-up driven by said engine which produces an output voltage waveform, a trigger circuit controlled by said pick-up to produce sparks when triggered, means for applying a bias to said output waveform, means for varying said bias up to a predetermined maximum in accordance with the amplitude of said waveform produced by said pick-up, said bias applying means and bias varying means further causing said trigger circuit to be triggered at a substantially constant point in said pick-up waveform up to a predetermined speed of said engine and for causing an advance in timing in proportion to increasing engine speed above said predetermined speed.

2. A spark ignition system for an internal combustion engine, comprising a trigger circuit having a normal bias to a first state, an engine driven pick-up coupled to the trigger circuit and which includes cyclical means which operates in a cycle for producing a voltage in opposition to said bias, means for overcoming said bias, at a point in said cycle dependent on engine speed, to drive the trigger circuit to a second state and so produce a spark, and means operable when the engine speed is below a predetermined value for modifying the input from the pick-up to the trigger circuit whereby the trigger circuit is driven to the second state at a substantially constant point on the pick-up waveform.

3. A system as claimed in claim 2 in which said voltage produced by said pick-up. comprises a positivegoing portion and a negative-going portion, and wherein said point occurs when the pick-up voltage is near its maximum.

4. A system as claimed in claim 3 further comprising a capacitor, said positive-going portion of said voltage produced by said pick-up being used to charge said capacitor, means for applying the resultant voltage thereof to the trigger circuit in opposition to the pickup voltage to obtain fixed timing, and means for modiengine speed the transistor saturates so that the capacitor charges to supply voltage.

7. A system as claimed in claim 6 including capacitor means in the base circuit of said transistor for modifying the advanced characteristics.

8. A system as claimed in claim 4 wherein said capacitor is charged by said positive going output of said pick-up, the negative going pick-up output producing the required sparks. 

1. A spark ignition system for an internal combustion engine comprising a pick-up driven by said engine which produces an output voltage waveform, a trigger circuit controlled by said pick-up to produce sparks when triggered, means for applying a bias to said output waveform, means for varying said bias up to a predetermined maximum in accordance with the amplitude of said waveform produced by said pick-up, said bias applying means and bias varying means further causing said trigger circuit to be triggered at a substantially constant point in said pick-up waveform up to a predetermined speed of said engine and for causing an advance in timing in proportion to increasing engine speed above said predetermined speed.
 2. A spark ignition system for an internal combustion engine, comprising a trigger circuit having a normal bias to a first state, an engine driven pick-up coupled to the trigger circuit and which includes cyclical means which operates in a cycle for producing a voltage in opposition to said bias, means for overcoming said bias, at a point in said cycle dependent on engine speed, to drive the trigger circuit to a second state and so produce a spark, and means operable when the engine speed is below a predetermined value for modifying the input from the pick-up to the trigger circuit whereby the trigger circuit is driven to the second state at a substantially constant point on the pick-up waveform.
 3. A system as claimed in claim 2 in which said voltage produced by said pick-up comprises a positive-going portion and a negative-going portion, and wherein said point occurs when the pick-up voltage is near its maximum.
 4. A system as claimed in claim 3 further comprising a capacitor, said positive-going portion of said voltage produced by said pick-up being used to charge said capacitor, means for applying the resultant voltage thereof to the trigger circuit in opposition to the pick-up voltage to obtain fixed timing, and means for modifying the effect of said capacitor on said pick-up voltage above the predetermined engine speed.
 5. A system as claimed in claim 4 further comprising voltage sensitive means for preventing charging of said capacitor above said predetermined engine speed.
 6. A system as claimed in claim 5 in which said voltage-sensitive means comprises a transistor with a base circuit, including means whereby below said predetermined engine speed the transistor charges the capacitor to a voltage determined by the pick-up voltage and less than the supply voltage, but above the predetermined engine speed the transistor saturates so that the capacitor charges to supply voltage.
 7. A system as claimed in claim 6 including capacitor means in the base circuit of said transistor for modifying the advanced characteristics.
 8. A system as claimed in claim 4 wherein said capacitor is charged by said positive going output of said pick-up, the negative going pick-up output producinG the required sparks. 